1994 jimmy 4.3 vortec has a stumble right off of idle when accelerating and a hesitation once and awhile at random spaads ussually under load any suggestions?

Posted / edited by AnonymousUser on : 17-12-2018

Answers :

Do you have an O2 sensor code that would explain a random miss?\015\012Does it happen cold or hot? Have you checked the spark from the coil?\015\012\015\012Diagnosis \015\012Before beginning any diagnosis and testing procedures, visually inspect the components of the ignition system and engine control systems. Check for the following: \015\012

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Discharged battery \015\012

Damaged or loose connections \015\012

Damaged electrical insulation \015\012

Poor coil and spark plug connections \015\012

Ignition module connections \015\012

Blown fuses \015\012

Damaged vacuum hoses \015\012

Damaged spark plugs

\015\012Check the spark plug wires and boots for signs of poor insulation that could cause crossfiring. Make sure the battery is fully charged and that all accessories are off during diagnosis and testing. Make sure the idle speed is within specification. \015\012If an open or ground in the Ignition Control (IC) circuit occurs during engine operation, then engine will continue to run, but using a back-up timing mode (controlled by the ICM) based on preset timing values. The Malfunction Indicator Lamp (MIL) or SERVICE ENGINE SOON light will not illuminate at the first appearance of a break in the circuit. However, if the IC fault is still present once the engine is restarted, a Code 42 will set on OBD 1 systems in the PCM and the MIL will illuminate. Poor performance and fuel economy may be noticed while the engine is running under back-up timing. \015\012When attempting to search for ignition troubles, keep in mind the various sensor inputs which the PCM uses to calculate timing may affect engine performance. The PCM will alter timing based on sensor inputs as follows: \015\012

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Low MAP output voltage = More spark advance \015\012

Cold engine = More spark advance \015\012

High MAP output voltage = Less spark advance \015\012

Hot engine = Less spark advance

\015\012With this in mind, DETONATION could be caused by low MAP output or high resistance in the coolant sensor circuit. POOR PERFORMANCE could be caused by a high MAP output or low resistance in the coolant sensor circuit.